#include <iostream>
#include <vector>
using namespace std;

int main()
{
    int n;
    cin >> n;
    vector<int> dp(n + 1);
    dp[0] = 0, dp[1] = 1, dp[2] = 2;
    for (int i = 3; i <= n; i++)
    {
        dp[i] = dp[i - 1] + dp[i - 2];
    }
    cout << dp[n] << endl;
    return 0;
}